The present invention relates to a safety cutoff power window control device.
As we know, power window control devices normally comprise a circuit supplied with an enabling signal from one or more switches, and which provides for correct polarity supply of one or more electric motors connected to, and for controlling opening or closing of, a respective window. If the device is designed for automatically controlling the opening and closing functions, the circuit provides for supplying the motor until opening or closing of the respective window is completed.
A major drawback of automatically controlled power windows is that, in the event of an obstacle impeding operation of the window (especially when closing it), considerable operating power is generated, which may possibly result in personal injury in the case of obstacles consisting of parts of the body.
By way of a solution to the above problem, automatic control devices feature a safety system, which detects the power generated by the motor (normally by measuring current absorption of the motor) and, over and above a predetermined threshold value, provides for briefly backing up and then stopping the window.
Unfortunately, however, the power required for closing the window varies in time, as well as at different points within the overall stroke of the window. In particular, the window guides may present local defects or unevenness, so that, for closing the window, greater power is required at certain points as compared with others within the overall stroke of the window. Other factors capable of seriously affecting the average power required for closing the window include temperature, particularly low temperatures resulting in freezing of the seals; and ageing of the seals resulting in impaired elasticity and possibly also distortion. In each of the above cases, a low threshold value may at times prevent the window from being fully closed by virtue of the required power being, at least at certain points or in certain situations, greater than the set threshold value. On the other hand, a high threshold value is ruled out for safety reasons.
One proposal already made for overcoming the time-dependent variation in the power required for closing the window is to measure the current absorption of the motor at the initial closing stage, and modify the threshold value accordingly on the basis of the measured value. On known devices of this type, the threshold value is assigned a given tolerance within which the closing power is considered acceptable, whereas the final closing stage is assigned a much higher tolerance to prevent activating the safety system which would otherwise prevent the window from being fully closed. According to this known solution, the threshold value may be represented by a straight line increasing from a minimum, when the window is fully lowered, to a maximum when the window is almost fully raised.
Though the above known solution does in fact provide for solving the problem of time-dependent variations in closing power due to atmospheric conditions or component ageing, the same cannot be said for variations occurring regularly during and at each stroke of the window.
Moreover, automatic power window devices are gradually becoming a standard feature of increasingly lower class vehicles, the poorer finish and workmanship of which increase the likelihood of high power points being misinterpreted as obstacles and so preventing troublefree operation of the window.